Evolution by natural selection





  • Adapt: organisms become better suited to environmental conditions via heritable (genetic) change over generations.



  • There is a ying and yang between the environment and evolution
    • complementary forces that interact to form a dynamic system

Evolution by natural selection


Natural Selection: Differences among individuals in a population in survival and reproduction

















Organisms which are better suited to their environment survive and reproduce better, leading to a change in the average traits of a population over time

Evolution by natural selection


Natural Selection: Differences among individuals in a population in survival and reproduction


Fitness: Measure of ability to survive and reproduce


Adaption: A trait that confers an advantage in a particular environment that evolved via natural selection

What did Darwin mean by fitness?



  • Best suited for the environment
    • biggest? fastest? strongest? smartest?


  • He intended “fittest” to mean the members of the species best suited for the immediate environment
    • individual needs the most favorable traits to survive in the environment
    • environments can change at any time


  • Those lacking the favorable traits—the “unfit”—most likely won’t live long enough to pass down their unfavorable traits
    • those traits will be breed out of the population
    • ‘breeding out’ traits can take a long time

Conditions necessary for natural selection



  • Variation: Individuals in a population vary
    • mutation as ultimate source of variation
    • migration -> gene flow within species
    • hybridization -> introgression across species




  • Heredity: Offspring resemble parents
    • DNA as primary mechanism of heredity


  • Differential survival or reproduction: Not all individuals survive, those with favorable traits survive and reproduce

Ways of studying adaptation


Ways of studying adaptation


Ways of studying adaptation


Advances in DNA sequencing


Advances in DNA sequencing


Advances in DNA sequencing


Advances in DNA sequencing


Advances in DNA sequencing



We can also now do genetic studies without harming any animals

Real world example: reivisting the white sands


Evolution by natural selection



The dunes are a dramatic selection environment

Evolution by natural selection



The dunes are a dramatic selection environment

Evolution by natural selection



Concealing coloration for predation avoidance

Color traits selected differently across variable landscapes


Natural selection: ruling out plasticity (w/ common gardens)


Natural selection: measuring selection in nature


Enclosure experiments

Natural selection: measuring selection in nature


Natural selection: measuring selection in genome


Natural selection: measuring selection in genome


Natural selection: measuring selection in genome


Natural selection: apply findings across species